1. Field of the Invention
The present invention relates to an optical switch array used for mutual connections in a communication network or between parallel computers.
2. Related Background Art
A switch array is an indispensable element in the fields of communications and computer technologies, but it is not easy to manufacture a large switch array even if state-of-the-art semiconductor techniques are used. In particular, although a crossbar switch is desired in favor of its characteristics, only a switch of this type for connecting a small number of terminals is available since the number of switches is increased.
An attempt has been made to manufacture a large crossbar switch by utilizing optical techniques. An example is described in IEEE SPECTRUM, Trudy E. Bell, August issue, first column, 1986, pp. 34-57. FIG. 1 is a schematic view showing a conventional optical crossbar switch. Four light sources 1.sub.1 to 1.sub.4 are driven by independent terminals (not shown). Output light beams 2 from the light sources 1.sub.1 to 1.sub.4 respectively serve as transmission beams 4 passing through a shutter array 3. Four photodetectors 5.sub.1 to 5.sub.4 receive the transmission beams 4 and transmit signals which represent light-receiving states to independent terminals (not shown), respectively.
This example shows a 4.times.4 optical crossbar switch. Signals from the independent terminals are sent to the light sources 1.sub.1 to 1.sub.4. The output beams 2 from the light sources 1.sub.1 to 1.sub.4 are spread in a vertical direction, and the fan beam is incident on the shutter array 3. The transmission beams 4 passing through light-transmitting portions of the shutter array 3 which are indicated by hatched portions are converged in a horizontal direction, and focused beams are respectively incident on the photodetectors 5.sub.1 to 5.sub.4. The signals which represent the light-receiving states from the photodetectors 5.sub.1 to 5.sub.4 are sent to the independent terminals, respectively. The connecting states of the terminals are determined by the light-transmitting states of the shutters of the shutter array 3. For example, a beam from the light source 1.sub.1 is incident on the first column of the shutter array 3. In this case, when a shutter of the third row and the first column is set in a light-transmitting state, the beam is detected by the photodetector 5.sub.3. In this case, a terminal connected to the light source 1.sub.1 is connected to a terminal connected to the photodetector 5.sub.3. This can similarly apply to other terminals.
FIG. 2 is a block diagram of a network using a unidirectional switch array shown in FIG. 1. This network comprises transmission terminals 11.sub.1 to 11.sub.4, a unidirectional switch array 12, and four reception terminals 13.sub.1 to 13.sub.4. As indicated by arrows in FIG. 2, signals are sent from the transmission terminals 11.sub.1 to 11.sub.4 to the reception terminals 13.sub.1 to 13.sub.4 through the unidirectional switch array 12. Acknowledgement signals representing that the reception terminals received the signals, and data request signals are often required to be sent from the reception terminals 13.sub.1 to 13.sub.4 to the transmission terminals 11.sub.1 to 11.sub.4. With the above arrangement, however, reverse signal transfer cannot be performed.
FIG. 3 is a block diagram showing an arrangement of parallel computers using a unidirectional switch array. Four processors 21.sub.1 to 21.sub.4 are connected to each other through a unidirectional switch array 22. In this arrangement, the transmission terminal also serves as the reception terminal. Signals from the processors 21.sub.1 to 21.sub.4 are switched by the unidirectional switch array 22 and are selectively directed toward the processors 21.sub.1 to 21.sub.4. With this arrangement, it is possible to mutually transmit signals between the processors 21.sub.1 to 21.sub.4, but the mutual connecting capacity is degraded. Assume that a signal is sent from the processor 21.sub.1 to the processor 21.sub.4. The internal shutters of the unidirectional switch array 22 are so set as to send a signal from the processor 21.sub.1 to the processor 21.sub.4 by the unidirectional switch array 22. The unidirectional switch array 22 must reset the shutters so that a response signal such as an input data reception acknowledgement signal or the like is sent from the processor 21.sub.4 to the processor 21.sub.1. In this manner, the switches must be switched for the two processors so as to send signals between them.
A wasteful switching time is required, and an operation speed of the system is decreased, resulting in inconvenience. In addition, since switching must be performed in synchronism with the respective signals, control is cumbersome, and a control circuit is complicated.
A conventional bidirectional switch array arranged by using semiconductor elements is also known to those skilled in the art. FIG. 4 is a block diagram of a shared memory type parallel computers using such a bidirectional switch array. This computer system comprises four processors 31.sub.1 to 31.sub.4, a bidirectional switch array 32, and four memories 33.sub.1 to 33.sub.4. Any one of the processors 31.sub.1 to 31.sub.4 can access any one of the memories 33.sub.1 to 33.sub.4 through the bidirectional switch array 32. Signals sent from the processors 31.sub.1 to 31.sub.4 are typically address signals, and the memories 33.sub.1 to 33.sub.4 send back data signals to the processors 31.sub.1 to 31.sub.4 upon reception of the address signals.
The bidirectional switch array utilizing the semiconductor elements is, however, small and is not suitable for a system for performing signal transfer between a large number of terminals.